An untuned RF cavity using multifeed coupling

A ferrite-loaded untuned RF cavity was designed and fabricated as the accelerating structure for a compact proton synchrotron dedicated to cancer therapy. An invented power-feeding method, “multifeed coupling”, was used to achieve a gap voltage higher than 700 V with an applied RF power of 1.2 kW in the frequency range 1.5–8 MHz and a cavity length 0.4 m. The temperature in the ferrite cores had less than a 22°C rise from room temperature using only forced air cooling.